Lightly grease a large cookie sheet. Set aside.

In a large mixing bowl beat butter with
an electric mixer on medium speed for 30 seconds.
Add the sugar, cocoa powder, and baking powder;
beat until combined. Beat in the eggs.
Beat in as much of the flour as you can.
Using a spoon, stir in any remaining flour,
white baking bar, and semisweet chocolate.

Divide dough in half.
Shape each half into a 9-inch-long log.
Place logs about 4 inches apart on
prepared cookie sheet.
Flatten logs slightly until about 2 inches wide.

Bake logs in a 375° oven for 20 to 25 minutes
or until a wooden toothpick
inserted near the centers comes out clean.
Cool on the cookie sheet set on
a wire rack for 1 hour. Using a serrated knife,
cut each log diagonally into 1/2" thick slices.
Lay slices, cut sides down, on ungreased
cookie sheets.
Bake slices in a 325° oven
for 8 minutes. Turn slices over.
Bake for 7 to 9 minutes more or until slices
are dry and crisp. (Do not overbake.)
Transfer to wire racks and let cool.
Store in an airtight container at room temperature
for up to 1 week. Makes about 32 biscotti.

To make ahead:
Place cooled biscotti in a freezer container and
freeze for up to 3 months.
Thaw at room temperature before serving.